The euphoria surrounding completion of the first draft of the sequence
of the human genome signaled the beginning of the end of a historic phase
of biomedical research that spanned the 20th century—the creation of
an inventory of the molecules required for human life. Throughout the past
100 years, much knowledge was also learned about biological function but from
a historical perspective the big story was the molecular inventory. Like the
19th-century biologists, who enumerated the variety of biological species
and identified their phylogenetic relationships, 20th-century biologists used
genetics, biochemistry, and large-scale genome sequencing to identify the
catalog of human genes. Much work remains with this inventory because picking
all human genes from a sequence of 3 billion DNA base pairs is incomplete
and far from trivial. The initial count of 35 000 human genes may be
short of the actual number. In addition, many genes originate more than one
protein product owing to alternative splicing of the primary RNA transcript.
Thus, the number of different human proteins will likely exceed 100 000.